1. Field of the Invention
The present invention relates to a non-aqueous electrolyte battery incorporating magnesium serving as a charge carrier thereof.
2. Description of the Related Art
In recent years, great progress of lithium ion secondary batteries and nickel-hydrogen secondary batteries has been made. Thus, the foregoing batteries have widely been used in portable electronic apparatuses as secondary batteries having large capacities. Another secondary battery of a type incorporating magnesium ions or calcium ions as charge carriers thereof except for lithium ions has been reported.
As a secondary battery incorporating, for example, calcium ions serving as charge carriers, a non-aqueous electrolyte battery has been disclosed in Japanese Patent Laid-Open No. 6-163080. According to the disclosure, a carbon material, such as graphite or cokes, is employed as the negative-electrode active material. Moreover, a metal oxide containing calcium, such as CaCo2O4, Ca3Co4O9, Ca2Co2O5, Ca3Co3O6, CaFeO3 or CaFeO2, is employed as the positive-electrode active material. The foregoing non-aqueous electrolyte battery is expected to realize a capacity larger than that realized by lithium. To enlarge the capacity of calcium ion positive electrode per unit weight, a battery has been disclosed in Japanese Patent Laid-Open No. 8-321305 which incorporates a silicide or germanide of metal as the positive-electrode active material.
As a secondary battery incorporating magnesium ions as charge carriers, its possibility has been pointed by P. Novak in 1993 (J. Electrochem. Soc. Vol. 40, No.1, January (1993) 140). The disclosed battery incorporates TiS2, ZrS2, RuO2, Co3O4 or V2O5 as the positive-electrode active material thereof. Specifically, a system incorporating V2O5 as the positive-electrode active material and electrolytic solution prepared by dissolving Mg(ClO4)2 in acetonitrile has realized a capacity of 170 mAh/g. Then, a positive-electrode active material prepared by doping magnesium ions into MoO3 has been reported (M. E. Spahr;J. Power Source 54 (1995) 346).
The battery of a type incorporating the foregoing positive-electrode active material has diffusion paths for magnesium ions in positive electrode crystal in the form of a one-dimensional shape. Therefore, in general, magnesium ions cannot quickly be diffused. An influence of the foregoing slow diffusion deteriorates the load resistance and cycle operation resistance. Therefore, raising of the diffusion speed of magnesium ions and improvement in the cycle operation resistance have been required.
In view of the foregoing, an object of the present invention is to provide a non-aqueous electrolyte battery capable of raising the diffusion rate of magnesium ions and improving cycle operation resistance.
To achieve the foregoing object, according to one aspect of the present invention, there is provided a non-aqueous electrolyte battery comprising: a positive electrode containing LixMO2 (where M is an element containing at least Ni or Co) as a positive-electrode active material thereof; a negative electrode disposed opposite to the positive electrode and containing a negative-electrode active material which permits doping/dedoping magnesium ions: and a non-aqueous electrolyte disposed between the positive electrode and the negative electrode and containing non-aqueous solvent and an electrolyte constituted by magnesium salt, wherein the value of x of LixMO2 satisfies a range 0.1xe2x89xa6xxe2x89xa60.5.
The non-aqueous electrolyte battery according to the present invention has the structure that the value of x of LixMO2 employed as the positive-electrode active material satisfies 0.1xe2x89xa6xxe2x89xa60.5. Therefore, lattice spaces for accommodating magnesium ions can be obtained. Moreover, the diffusion paths for magnesium ions are formed into two-dimensional shape. Therefore, magnesium ions can quickly be diffused.
Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.